Blakeman re Panting-- and more discussion of what happened at the nest on April 17th

Every so often I clean out my mailbox and that is when I find letters that have fallen through the chinks. Here is such a one, from Karen Anne Kolling,dated April 21, 2005:

"Why, in the Field Notes, are Pale Male & Lola reported occasionally to be panting ? Is this heat-related?"

I remembered a previous letter from John Blakeman rejecting the possibility that extreme heat caused Lola to mantle the eggs in the nest on April 17th, the day we saw that behavi0r and thought that a chick had hatched. [Come to think of it, exactly a month ago from today!] When I brought up the extreme heat hypotheses, John noted that nobody had reported any panting. Now, coming across Karen Anne's question, I brought up the question again in an e-mail to John Blakeman. Here is my letter, and his response, which, I ought to say, finally convinced me that it was not the heat:

Dear John,

I was clearing out one of my e-mail mailboxes today and came across this question from a regular website correspondent. When you rejected my speculations that Lola's mantling on April 19th might have been egg-cooling occasioned by excessive heat I remember you said something about there being no reports of panting. Well, I think there have been such reports, as this note confirms. Also, I seem to remember seeing the female up there in the nest panting on very hot days in years past. You were assuming that when the temperature is, say, 85 degrees on street level it would be a bit cooler up there because of breezes. But if the sun is shining directly on the nest, and the air is very still, might it not be much, much hotter, indeed, broiling up there? I always thought so.

Marie


John replied:

Marie,

Red-tails parked out in the hot sun will pant, no doubt about that. They have dark, heat-absorbing feathers, and when perched in dead, hot air on sunny days, they will pant. Free birds then elect to soar into cool air, or perch in shaded tree vegetation. Incubating birds don't have a shaded alternative, and they just sit there and reduce internal body temperatures by panting.

But this panting is normal and minor. many times I've seen panting in red-tails resulting from excessive exertion, after prolonged hunting flights at fleeing prey on hot days. In this case, the mouth is widely gaped, with the tongue projecting upward and forward out of the mouth. That is the criterion for desperation panting. Was the tongue seen to be elevated and protruding? Or, was the mouth merely open and with only breathing contractions of the chest being seen? This is common on hot days in direct sun and does not indicate elevated body temperatures that could also be transmitted to eggs.

Even if Lola's body had elevated body temperatures, they could only have been a few degrees above the general 102-105 range, and this slight elevation would not directly elevate the egg temperatures. The only response needed by the hawk was to sit just slightly higher in the nest, reducing the surface area of the brood patch against the eggs.

There is no way the air up there was warmer than the eggs at near a hundred degrees. The only way this could have occurred would have been if the sun had heated the entire building surface below the nest and the air had risen directly through the nest. But because the nest was on the cornice, any rising air heated by direct contact with the building had to move around the sides and front of the cornice or curved ledge. Eddy currents would then form as the hot air moved over the roof rim, mixing in cooler air.

I can't conceive of conditions that would have elevated egg temperatures beyond normal incubation temps. All of the evidence I've seen still points to movements by a hatching egg that prompted the mantling, not inordinate nest temps.

How long did the mantling occur? If it was for a just moment or two, when there may have been a misunderstood prompt from the nest, causing the sitting bird to sit up and take a look. But when it did, it would have been back down on the eggs in just a minute or two as it perceived the eggs and/or young to be cooling without the brood patch contact.

There is no way the air temperature up there was around a 100 degrees. In fact, the building itself probably suppressed the air temperature at the nest. Yes, on a hot August day the stone of the building facade could become quite hot. But that's because it would have been in hot weather and sun for most of the summer. In April, the stone facing had just been at reasonably normal seasonal temperatures, retaining a cool spring thermal inertia. The seasonally cold stone easily absorbed the sun's heat without any significant warming. It takes a lot of joules of energy to heat thick, cold stone. A day or two of low April sunshine can't do much such stone building warming.

I'm still not convinced that the mantling behaviors resulted from elevated air temperatures. Mantling, and especially the direct peering into the nest cavity, all point to a hatched or broken egg that revealed movements by a little eyass. Parents never peer longingly at immobile eggs, only at things moving in the bottom of the nest.

I wish it weren't so, but all the evidence still points in the direction of a moving eyass in the nest, perhaps cracked out prematurely by the sitting parent who repeatedly kicked a metal prong that failed to respond in the manner of a normal stick.

Sincerely,

John A. Blakeman